Milk contains proteins such as caseins. The caseins are specifically useful for cheese-making, due to their ability to coagulate. Accordingly chemical methods for determining the content of casein in milk are known. They are however time consuming. Further, It is known to determine the casein content in milk directly by fast infrared analysis methods. However, the accuracy of these methods depends on the match between the calibration samples applied for the calibration of the infrared analysis instrument and the routine samples for which the content of casein is to be determined.
The purpose of the present invention is to propose a method, which is more universal, such as independent of the origin of calibration samples, than the known infrared analysis.
In the present description the word “milk” relates to the milk sample to be analysed. The words “liquid phase” and supernatant are used for the remaining portion of the milk sample after a separation of the casein. The supernatant contains whey-protein. Supernatant is in this description intended also to address the case when the liquid phase in fact is a filtrate.